Research Of Making Ice Particles At Cryogenic Atmosphere And Paint Stripping By Ice Jet

Ice jet technology shows a promising prospect of application and extension insurface cleaning and depainting engineering because of its environment-friendlyfeature. Aimed at development and design of an effective equipment producing iceparticle, this dissertation presented mainly a comprehensive study of the ice particleproduction through experimentation and numerical methods using computational fluiddynamics and computational heat transfer and a systemic research on the depaintingby use of ice blasting technology.According to the in-depth discussions about the thermal physical properties,mechanical performance and surface behavior of ice, a conclusion could be drawn thatthe ice particles with the temperature of-27℃～-60℃should be produced for iceblasting. An "ice sphere" physical model was established and the correspondingnumerical equations were solved to obtain the basic factors influencing the freezingprocess of a water droplet. The results showed that a water droplet of0.15mm indiameter had changed into ice particle with temperature of-50℃at a falling distanceof0.4m in the atmosphere with temperature of-60℃. In order to create a cryogenicatmosphere, liquid nitrogen was used. A numerical model describing the evaporationprocess of liquid nitrogen droplets was solved to obtain the basic laws of evaporation.Furthermore, the evaporation of atomized liquid nitrogen in a specific volume wassimulated.Based on the numerical analysis of freezing of a water droplet and evaporation ofthe atomized liquid nitrogen, an experimental apparatus was established.Experimental research was made to find basic laws of producing ice particles. Resultsshowed that ice particle, ranged from0.425mm to0.075mm in diameter, withtemperature below-30℃were produced continuously by use of the apparatus.The accelerating process of ice particles in a conventional industrial siphon-typesand blasting nozzle were investigated numerically in detail. The numerical equations,including conservation equations of mass, momentum and energy of gas phase, werebuilt based on compressible fluid dynamics. The turbulent flow characteristic wasintroduced by means of RNG k-ε turbulence model and the gas-solid interactions werereflected by discrete phase model.The applications of ice blasting technology in the industrial field of depaintingwere investigated experimentally in the last part of the dissertation. The substrates of depainting samples were aluminum alloy (2A11) and poly propylene. The acrylicpaint was sprayed on the substrate surfaces. The depainting experimental resultsshowed that gas pressure of the ice jet was the most important working parameterinfluencing the de-painting effect. Even at0.2MPa blasting pressure, the two kinds ofpaint coatings samples were stripped effectively. SEM pictures showed that polypropylene surface was roughened obviously when the blasting pressure was above0.3MPa, but the aluminum alloy surface changed little under different blastingconditions.